1. Field of the Invention
The present invention relates to an endoscope light source unit suitable for an endoscope or an electronic endoscope, etc.
2. Description of the Related Art
Recent electronic endoscope systems have provided therein a processor with a built-in light source unit for lighting, to which an electronic scope having an electronic camera mounted on the distal end thereof or a fiber scope for conducting observation only through optical members is connected for use. In particular, electronic scopes have been provided for use with a wide variety of thicknesses and functions suited to different locations of observation. Processors connectable with various types of electronic scopes and fiber scopes must also have light source units that are compatible with such various electronic scopes and fiber scopes. For this reason, conventional light source units have been constructed so as to supply necessary amounts of illumination light to electronic scopes that require a maximum light quantity.
Such light source units are configured such that illumination light emitted from a high-intensity lamp is condensed by a condenser lens and made incident on the incident end face of a scope light guide (typically an optical fiber bundle). Since the necessary quantity of illumination light varies in accordance with the type of electronic scope and with the observation location, the light source units are equipped with an aperture device for mechanically adjusting the amount of light. Among known aperture devices is one that includes a diaphragm which is composed of a partly-notched portion and an arm portion integrated with the partly-notched portion, having a size such that all the light from a light source lamp can be blocked, and a motor mechanically connected to an end of the arm portion. The motor is rotated to turn the diaphragm about the top of the arm portion, thereby changing the degree of illumination light blocked by the partly-notched portion to adjust the illumination quantity (see Japanese Patent Laid-Open Publication No. 2003-305008). Moreover, a light shielding plate may be provided with a plurality of aperture openings having different opening ratios or transmittances so as to form a rotary aperture plate which regulates the amount of light incident on the incident end face of a light guide by putting one of the aperture openings selectively between a light source unit and the incident end face of the scope light guide (i.e., into the illumination optical path).
Such a light source unit uses high-intensity lamps such as a metal halide lamp or a xenon lamp. The higher intensities the lamps have, the more heat components the illumination light contains. Consequently, depending on the type of scope, the light source unit may be excessively intense, and also may heat up the end of the scope due to the heat components of the illumination light unless the quantity of the light source unit is turned down (reduced). Some light source units adjust picture brightness without activating aperture devices but by adjusting the electronic shutter speed. In such a light source unit, pictures (images) of appropriate brightness can be obtained by increasing the electronic shutter speed, whereas an excessively high quantity of the illumination light can heat up the end of the light guides, i.e., the distal end of the scope.